The invention relates to annular seal assemblies used for preventing leakage in hydraulically extended and retracted multi-staging cylinders.
Hydraulic cylinders having a number of nested thin wall tubes with annular seals between the tubes are well known. The cylinders define an interior hydraulic fluid chamber which is connected to a source of hydraulic fluid so that flow of fluid into the chamber extends the cylinder and exhausting of fluid from the chamber allows retraction of the cylinder tubes.
Annular seal assemblies are conventionally provided between adjacent tubes in the cylinder. These seal assemblies must maintain a reliable hydraulic seal between the outer surface of the inner tube and the inner surface of the outer tube, despite changes in the pressure of the hydraulic fluid and relative movement of the tubes. Disassembly of the cylinders to replace failed seal assemblies is difficult and time consuming. For this reason, it is desirable that the seals have a long useful working life.
Conventional seals for thin wall hydraulic cylinder tubes have an unsatisfactory short useful life. During useful life, the sealing surfaces are moved axially along the tubes as the cylinder is extended and retracted. When the cylinder tubes move under high hydraulic pressure the seals are subjected to wear which, in time, degrades the efficiency of the seals. Further, thin wall multi-tube cylinders are flexed by side loads and can leak because the conventional seals are insufficiently compliant to maintain a seal between flexed cylinder tubes.
Also, conventional seal assemblies include annular sealing members confined in seal grooves with outer and inner surfaces engaging adjacent tubes. When the tubes are moved axially relative to each other, particularly when the hydraulic fluid in the cylinder is under high pressure, there is a considerable frictional force exerted on the sealing member by the moving tube. This force can roll the sealing member in the seal groove and destroy the ability of the member to maintain a hydraulic seal between the cylinders. In this event, the seal fails and must be replaced.
Accordingly, there is a need for an improved seal assembly for maintaining both low pressure and high pressure seals between tubes of a multi-tube hydraulic cylinder. The seal assembly should have a long useful life and the ability to maintain the seal despite increase of the gap between the cylinder tubes due to lateral loading of the cylinder. The seal should also prevent rolling of sealing members due to frictional forces generated by relative movement of the tubes.
The invention is an improved annular seal assembly including an annular primary seal member and an annular base seal member. The primary seal member is formed from relatively soft elastomer material and includes inner and outer radial pressure ribs which engage the bottom of the seal recess and the wall of an adjacent tube to form a low pressure seal. The ribs are pressure biased against the surfaces to improve the seal as hydraulic fluid pressure increases. The primary seal member between the ribs is exposed to the hydraulic fluid chamber so that pressure of the fluid biases the ribs against the adjacent walls. The primary seal member is mounted on the base seal member so that as pressure of the hydraulic fluid increases the fluid biases a second set of seal ribs on the base seal member against the adjacent walls to establish a high pressure seal. The base seal member is made from elastomer material harder than the material used in the primary seal member.
The base seal member has an axial length approximately twice its radial width and a heel located away from the pressure fluid and facing the adjacent tube. The heel is compressed into the base seal member to squeeze the outer end of the base seal member between the two surfaces and hold this end in place to prevent rolling of the base member in the seal groove when the tubes are moved along each other.
The primary and base seal members assure that reliable pressure seals are maintained as pressure in the cylinder increases from relatively low pressure, which is sealed by the primary seal member, to higher pressure which is sealed by the base seal member. The seal length of the base seal member, the heel at the outer end of the base seal member and the mechanical connection between the base seal member and a tube bearing member cooperate to prevent rolling of the base member in the seal groove.
The seal assembly holds the base seal member in proper orientation within the seal groove to assure a long useful life. Additionally, the seal assembly has sufficient radial compliance to maintain a seal between the adjacent walls of the seal groove and adjacent tube, despite increasing of the gap between these walls due to ovalization of the tubes. Ovalization occurs when a lateral load is applied to the end of the cylinder and tends to rotate one tube relative to another tube at the seal assembly.
Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings illustrating the invention, of which there are three sheets and three embodiments.